RUI: Probing the Structure of Excited Baryons that Decay through the Omega-Meson Channel

这种强作用力产生了核引力，将质子和中子（也就是核子）结合在一起。准确理解强核力是如何在原子核内部产生的，是当今核物理学面临的最大智力挑战之一。我们知道强力是由胶子的粒子交换介导的，胶子的相互作用占了核子质量的大部分。核子本身是由另外三种被称为夸克的粒子组成的，这些粒子嵌在泡沫般的胶子海洋中。然而，我们对质子和中子是如何由夸克和胶子组成的了解，充其量也只是初步的。一个高能粒子，如电子或介子，入射到一个核子上，可以直接与其中一个夸克相互作用，激发夸克产生更高的能量，使核子质量更大。这些激发态只存在极短的瞬间，大约是一万亿分之一秒的数量级，然后衰变成其他粒子。产生的粒子的类型以及它们在空间中的分布方式提供了关于核子组成的关键信息。该奖项授予拉马尔大学，一个主要的本科院校，支持本科生作为研究人员的指导，并为他们进入研究生院和/或行业做准备。每年夏天，两到三名本科生将在托马斯·杰斐逊国家加速器设施现场工作十周，协助实验室正在进行的两个实验的硬件和软件项目。为这项工作提供的培训包括学习如何设置计算机系统，编写高效的软件，运行检测器模拟，以及在计算机集群（如拉马尔大学的高性能计算机集群）上安排大规模计算。通过他们的实践经验，本科生将了解检测器实际工作的细微差别和复杂性。拥有良好的硬件技能将对数据分析最终结果的可靠性有深刻的见解，这是研究生院以及处理大数据和数据分析的行业所高度追求的技能。学生们还将学习时间管理的软技能和团队合作的整体重要性。该奖项支持在杰斐逊实验室（美国），ELSA（德国）和J-PARC（日本）通过使用线性偏振光子，极化电子和介子（π+/π -）束来研究核子的基本性质和结构。强核相互作用导致了从夸克与胶子的结合、夸克与无色强子的结合、核子与原子核的结合以及大原子核的集体行为等大距离尺度上的现象。PI和他的团队将寻求以下问题的答案：当海夸克和胶子的贡献最小时，价夸克是如何自组装的，胶子如何附着在夸克上以增加当前夸克的质量到组成夸克的质量，以及夸克如何在核子内部共振以形成夸克的激发态集合。该小组旨在了解夸克和胶子集合的涌现行为和结构。在JLab和ELSA的案例中，这些研究的探针将是介子。通过欧米茄介子的清晰和明确的信号探测N*共振的结构有很大的发现潜力。此外，对于电磁通道来说，通过ω模式衰减的重子共振作为Q2的函数的数据非常缺乏，这是理解强子质量出现所需要的。π将使用耦合通道方法来处理介子束数据，以确定并协助进行双介子衰变通道的振幅分析，这对于理解强子质量的出现是进一步必要的。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The strong force gives rise to the nuclear attractions that bind protons and neutrons, otherwise known as nucleons, together inside the nucleus. Understanding exactly how the strong nuclear force is generated inside the nucleus is one of the greatest intellectual challenges facing nuclear physics today. We do know that the strong force is mediated by the exchange of particles known as gluons, and it is this gluon interaction that accounts for most of the mass of the nucleon. The nucleons themselves are formed of three other particles called quarks embedded in a frothing sea of gluons. Our knowledge of how protons and neutrons are constructed from their quark and gluon constituents, however, is rudimentary at best. An energetic particle, such as an electron or a pi-meson, incident on a nucleon can interact directly with one of the quarks inside, exciting the quark to higher energy, making the nucleon more massive. These excited states exist for the briefest of moments, on the order of a trillionth of a trillionth of a second, and then decay into other particles. The types of particles produced and how they are distributed in space provide key information on the make-up of the nucleon. This award to Lamar University, a Primarily Undergraduate Institution, supports the mentoring of undergraduate students as researchers and their preparation for graduate school and/or industry. Two or three undergraduate students will work onsite at the Thomas Jefferson National Accelerator Facility for ten weeks each summer to assist in hardware and software projects at two of the ongoing experiments at the Laboratory. The training provided for this work includes learning how to set up computer systems, writing efficient software, running detector simulations, and scheduling large-scale computations on a computer cluster like the High Performance Computer Cluster at Lamar University. Through their hands-on experience, the undergraduate students will learn the nuances and intricacies of how detectors actually work. Having good hardware skills will give profound insight into the reliability of the final results from data analysis, skills that are highly sought after by graduate schools as well as by industries that deal with big data and data analytics. The students will also learn the soft skills of time management and the overall importance of working together in a team.This award supports the study of the fundamental properties and structure of nucleons through using a beam of linearly-polarized photons, polarized electrons and pions (π+/π–) at Jefferson Lab (USA), ELSA (Germany), and J-PARC (Japan). The strong nuclear interaction is responsible for phenomena over a large distance scale from the binding of quarks by gluons, the combinations of quarks into colorless hadrons, the binding of nucleons into nuclei, and the collective behavior of large nuclei. The PI and his group will seek answers to questions such as how valence quarks self-assemble when sea quark and gluon contributions are minimal, the nature of how gluons attach to quarks to increase the mass of current quarks to that of constituent quarks, and how quarks resonate inside the nucleon to form excited assemblies of quarks. The group aims to understand the emergent behavior and structure from assemblies of quarks and gluons. In the case at JLab and ELSA, the probe for these studies will be the omega meson. There is great discovery potential in probing the structure of N* resonances through the clean and unambiguous signal of the omega meson. Moreover, there is a significant dearth of data of baryon resonances decaying through the omega mode as a function of Q2 for the electromagnetic channels, which is needed to understand the emergence of hadron mass. The PI will use a coupled-channel approach to the pion-beam data to ascertain and assist in amplitude analysis for the two-pion decay channel, which is further necessary for understanding the emergence of hadron mass.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.